1. Field of the Invention
The present invention relates to a fluid mixing device used for a gene analysis and the like and, in particular, to a fluid mixing device constructed as a micro chip.
2. Description of the Related Art
In a field referred to as a μTAS (Total Analysis System), a flow channel and a storage tank are formed in a substrate made of glass or plastics (hereinafter referred to as “micro chip”) and a sample or a reagent is tested or analyzed by treating the sample or the reagent in the flow channel and the storage tank.
When the sample or the reagent is tested or analyzed by the use of the micro chip, the sample or the reagent is supplied to the flow channel and the storage tank of the micro chip from the outside of the micro chip. Further, the sample or the reagent supplied to the flow channel and the storage tank has pressure applied thereto from the outside of the micro chip, whereby the flow of the sample or the reagent is controlled and the treatment of stirring or mixing the sample or the reagent is performed.
In order to apply pressure to the sample or the reagent from the outside of the micro chip, the micro chip, a unit for supplying pressure for controlling an operation, and a unit for supplying a sample or a reagent are connected to each other by a tube or the like (see JP 2005-345463 A (patent document 1) and JP 2007-187616 A (patent document 2)).
FIG. 1 is a schematic view of a related micro chip mixing first liquid 1a that includes a sample or a reagent to be tested or analyzed with second liquid 1b that is different from first liquid 1a. 
As shown in FIG. 1, the micro chip has first supply tank 2a for supplying first liquid 1a and second supply tank 2b for supplying second liquid 1b that is different from first liquid 1a. Further, in the micro chip is formed mixing tank 9 for mixing first liquid 1a with second liquid 1b. 
Furthermore, the micro chip is provided with first mixing tank flow channel 3a for feeding first liquid 1a from first supply tank 2a to mixing tank 9, and at a position different from a position where first mixing tank flow channel 3a is formed, the micro chip is provided with second mixing tank flow channel 3b connecting second supply tank 2b to mixing tank 9. First supply tank 2a and second supply tank 2b are connected respectively to a liquid supply unit (not shown) supplying liquid and a pressure supply unit (not shown) supplying pressure for controlling an operation through a tube.
When pressure applied to first liquid 1a in first supply tank 2a is increased, first liquid 1a is fed to mixing tank 9 through first mixing tank flow channel 3a. In the case where the amount of first liquid 1a that is fed is more than an allowance of mixing tank 9 or in the case where vibration is applied to the micro chip, first liquid 1a is fed to second supply tank 2b through second mixing tank flow channel 3b that is connected to mixing tank 9 and that is different from first mixing tank flow channel 3a. Second supply tank 2b is supplied with second liquid 1b, so that first liquid 1a is mixed with second liquid 1b in second supply tank 2b. 
Depending on the purpose of the test or the analysis, there is a case where the mixing of first liquid 1a with second liquid 1b in a place other than mixing tank 9 is not allowed. Thus, second mixing tank flow channel 3b is provided with second valve 5b preventing first liquid 1a fed to mixing tank 9 from flowing toward second supply tank 2b through second mixing tank flow channel 3b. 
Further, similarly, first mixing tank flow channel 3a is also provided with first valve 5a preventing second liquid 1b from flowing toward first supply tank 2a from mixing tank 9 through first mixing tank flow channel 3a. In this way, by appropriately providing respective mixing tank flow channels 3a, 3b with first valve 5a and second valve 5b, it is possible to prevent first liquid 1a from mixing with second liquid 1b in a place other than mixing tank 9.
As the valve preventing the flow from the mixing tank to the supply tank as described above, there is employed a passive valve utilizing flow resistance or a valve using a flexible material such as a diaphragm.
The passive valve utilizing flow resistance has a structure such that a flow channel is provided with a portion having a reduced cross-sectional area to make a flow resistance value very large, thereby making liquid flow only when the liquid is fed by pressure exceeding this flow resistance value (see JP 2003-190751 A (patent document 3) and JP 2006-142448 A (patent document 4)).
In the example of the related micro chip shown in FIG. 1, a case where passive valves are employed as first and second valves 5a, 5b will be described.
In the case where first liquid 1a is fed from first supply tank 2a to mixing tank 9 through first mixing tank flow channel 3a, pressure exceeding the flow resistance value of first valve 5a is applied to first liquid 1a in first supply tank 2a. As a result, first liquid 1a passes through first valve 5a. First liquid 1a is fed to mixing tank 9 in the state where the pressure of first liquid 1a is reduced by first valve 5a. 
In the case where the amount of first liquid 1a that is fed exceeds the allowance of mixing tank 9, first liquid 1a is fed from mixing tank 9 toward second supply tank 2b for supplying second liquid 1b through second mixing tank flow channel 3b. When the pressure of first liquid 1a at second valve 5b is less than the flow resistance value of second valve 5b, first liquid 1a is stopped at second valve 5b. Thus, first liquid 1a is not fed from mixing tank 9 toward second supply tank 2b. 
In the case where a passive valve is used as a valve preventing a flow from a mixing tank to a supply tank, the passage of liquid through the valve is controlled only by the pressure of the liquid. This eliminates the need for providing a physical force or an electric signal for opening or closing the valve from the outside of the micro chip, which results in providing an advantage of easing the handling of the micro chip.
In a valve using a flexible material such as a diaphragm, the flexible material is deformed by the physical force or the electric signal provided from the outside of the micro chip to thereby open or close a flow channel.
In the example of the related micro chip shown in FIG. 1, a case will be described in which valves using a flexible material are employed as first valve 5a and second valve 5b. 
In the case where first liquid 1a is fed from first supply tank 2a to mixing tank 9 through first mixing thank flow channel 3a, first valve 5a is opened and second valve 5b is closed by a physical force or an electric signal provided from the outside of the micro chip. Thus, even in the case where the amount of first liquid 1a that is fed exceeds the allowance of mixing tank 9, the feed of first liquid 1a from mixing tank 9 to second supply tank 2b is stopped by second valve 5b. As a result, the feed of first liquid 1a to second supply tank 2b can be prevented.
In the case where the valve preventing the flow from the mixing tank to the supply tank is formed of a flexible material, the flow channel is opened or closed by deformation of the flexible material. This can reduce the possibility that the liquid leaks from the valve and hence can provide high reliability in the control of liquid (see JP 2003-139660 A (patent document 5) and JP 2003-139662 A (patent document 6)).
In the above example, description has been made on the assumption that as a method for controlling liquid in a supply tank, the feed of the liquid is not controlled but the pressure of the liquid is controlled. In addition to controlling the pressure of the liquid, controlling the liquid can be also performed by the amount of liquid that is fed by the use of a syringe pump or the like capable of controlling the amount of liquid that is fed in the supply tank. Even if the syringe pump is used, the amount of liquid that is fed and the capacities of the flow channel, the supply tank, and the mixing tank cannot be sufficiently controlled, so that it is surely thought that the amount of liquid that is fed to the mixing tank exceeds the allowance of the mixing tank to thereby cause the flow of the liquid from the mixing tank to the supply tank. Thus, even in the case where a flow rate is controlled by the use of the syringe pump or the like, a valve is required.
In the related micro chip shown in FIG. 1, in the case where a valve preventing the flow from the mixing tank to the supply tank is constructed by the use of a passive valve, the pressure of first liquid 1a needs to be equal to or more than a flow resistance value of first valve 5a and to be less than a flow resistance value of second valve 5b. In other words, this requires high accuracy pressure control and may reduce the operability of the micro chip.
In the case where the control of pressure to be applied to first liquid 1a does not satisfy a required accuracy, there is a possibility that the pressure of first liquid 1a is insufficient for the flow resistance value of first valve 5a or exceeds the flow resistance value of second valve 5b. In other words, there is a possibility that feeding the liquid to mixing tank 9 and preventing the flow of the liquid to the second supply tank 2 are not normally performed to thereby reduce the reliability of the micro chip.
Further, in the case where the valve that prevents the flow of the liquid from the mixing tank to the supply tank is constructed of a flexible material, there is a need to provide an external mechanism applying a force to the flexible material from the outside of the micro chip. Thus, the connection of the external mechanism to the micro chip is increased to thereby make the handling of the micro chip cumbersome, which may reduce productivity. Further, since the external mechanism is newly provided, there is also presented a problem in which the maintenance and the inspection of the external mechanism are newly required.